1. Field of the Invention
This invention relates to fast curing epoxy resin compositions. This invention also relates to two-part epoxy resin compositions which cure rapidly at room temperature and exhibit superior toughness.
2. Description of the Prior Art
Epoxy resins, i.e., organic compounds having one or more terminal or pendant oxirane groups ##STR1## have been widely used for many years in compositions for making adhesives, coatings, and molded, cast and potted products because of the relative ease with which they can be converted to cured solid products that are strong and resistant to many chemical environments. These epoxy resins may be cured using such curing agents as polyamide, polyamine, urea, phenolic and substituted phenolic curing agents, Lewis acid curing agents and carboxylated curing agents. Although the polyamine and polyamide curing agents are effective for curing the epoxy resins at room temperature, the cure rate is undesirably slow for many specific curing agents and end uses. To overcome this deficiency, the addition of certain catalysts to epoxy compositions has been described. U.S. Pat. No. 4,389,515 and U.S. Pat. No. 4,397,998 disclose rapid curing of epoxy resins for use in injection molding using a curing combination of an amino compound containing at least three amino hydrogens as curing agent, a Group I or Group II metal nitrate, iodide, thiocyanate, alkoxide or perchlorate as catalyst and polyalkylene ether glycol as stabilizer/solvent. U.S. Pat. No. 4,026,858 discloses accelerated curing of epoxy resins by use of aromatic or cycloaliphatic polyamines as curing agent and magnesium, calcium, zinc, manganese, cobalt or nickel perchlorate as catalyst. U.S. Pat. No. 4,101,459 discloses accelerated curing of epoxy resins by use of aromatic, heterocyclic or cycloaliphatic polyamines as curing agent and salts of trifluoromethanesulfonic acid as a catalyst. U.S. Pat. No. 4,130,511 discloses accelerated curing of epoxy resins by use of aromatic polyamides as curing agent and magnesium nitrate or a nitrate of an at least divalent metal of Group IIB, IIIB, IVB, VIB, VIIB or VIII as a catalyst. U.S. Pat. No. 4,112,231 discloses condensation of epoxides with organic compounds having an active hydrogen atom in the presence of a neutral organic salt such as sodium fluoborate, magnesium perchlorate, calcium perchlorate, manganese perchlorate, nickel perchlorate and zinc perchlorate. U.S. Pat. No. 3,018,262 discloses curing epoxy resins with metal salts of inorganic acids to provide fabric finishes for imparting crease and shrink resistance. U.S. Pat. No. 3,454,436 discloses promoting the cure of epoxy resins by polyamine curing agents by including lithium perchlorate as a catalyst to provide solid rocket propellant.
The incorporation into epoxy resins of epoxy resin-insoluble modifiers to reduce brittleness to shock has been described. U.S. Pat. No. 3,496,250 discloses the blending of an acrylonitrile butadiene-styrene graft polymer into epoxy resins to impart flexibility, shear strength and impact characteristics to cured epoxy resin.